vitest-testing

Vitest Testing — Server Reference

⚠️ This skill is server-focused. Frontend tests follow frontend-testing (Testing Library + six core principles). This file covers DB / socket.io server-side / CLI process patterns only.

Stack: vitest 4.x, TypeScript, ESM, better-sqlite3, socket.io-client

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Test Organization

• One test file per source file: foo.ts → src/__tests__/foo.test.ts
• Use describe to group by class or feature; it for individual behaviors
• Name tests as behavior assertions: 'creates a session with a unique id'

describe('MyService', () => {
  it('returns null when not found', () => { ... });
  it('throws when input is invalid', () => { ... });
});

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Setup / Teardown

• beforeEach — use for state that must be fresh per test (DB, server, sockets)
• beforeAll — use only for truly shared, read-only fixtures (e.g. static config)
• Always clean up servers and connections in afterEach to prevent port leaks

In-memory SQLite pattern (DB tests):

beforeEach(() => {
  db = createDatabase(':memory:');
  migrate(db, { migrationsFolder });
  store = new DrizzleSessionStore(db, sessions);
});

Socket.io integration pattern:

beforeEach(async () => {
  httpServer = createServer();
  io = new Server(httpServer);
  handler.register(io);
  await new Promise<void>((r) => httpServer.listen(0, r));
  const { port } = httpServer.address() as AddressInfo;
  clientSocket = ioc(`http://localhost:${port}`, { transports: ['websocket'] });
  await new Promise<void>((r) => clientSocket.on('connect', r));
});

afterEach(async () => {
  clientSocket.disconnect();
  io.close();
  await new Promise<void>((r) => httpServer.close(r));
});

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Test Double 選擇（server）

優先選低層級 double（真實實作接近度高 → 測試信心高）：

層級	方式	用途	範例
1	真實實作	可用 in-memory / 真的 server/socket 時優先	:memory: SQLite、真的 http.createServer + socket.io server、real repositories
2	Spy	觀察真實方法呼叫但不改行為	vi.spyOn(logger, 'warn') — 方法照跑，可驗證被呼叫
3	Fake	保留行為的簡化實作（共用 harness）	createFakeSummoner().claude() / FakeSummoner — 見 fake-summoner-server / fake-summoner-client skill；in-memory DrizzleSessionStore
4	Stub	固定回傳值，無邏輯	vi.fn().mockResolvedValue(fixedResult) — 窄介面、純 query
5	vi.mock	整個模組替換	無法 inject 的依賴（child_process、node-pty、fs/promises）